1. Field of the Inventions
The present inventions relate generally to injection molded articles used in optical applications. Such articles can include optical lenses and optical discs. More specifically, the present inventions relate to methods and apparatuses for producing net-molded optical articles that are formed so as to reduce and/or eliminate optical distortion along the peripheral edges thereof through differential cooling of the injection molded article.
2. Description of the Related Art
Injection molded articles that are used in optical applications must be formed as bubble-free bodies having accurately contoured, optically smooth outer surfaces. Generally, such articles are made from a synthetic resin and are molded to a desired final shape. As such, articles such as optical discs for data storage and eyewear lenses, including ophthalmic lenses, can be made quickly, inexpensively, and provide various desirable physical characteristics.
The injection molding process has the following basic steps: plasticizing, injection, chilling, and ejection. These steps are distinct from each other and must each be properly performed in order to ensure that an accurately-dimensioned and optically-acceptable article is produced using the injection molding process.
During the plasticizing step, a material, such as a polymer, is heated until the material is melted. The plasticizing step converts the material from its normal hard, often granular, form at room temperature to a liquid having a consistency necessary for use in the injection molding process at its correct melt temperature. The plasticized material is then injected into a mold until it completely fills the mold cavity.
After the mold cavity is completely filled, the material is allowed to cool. In this step, often called chilling, heat is removed from the plasticized material to convert it from a liquid consistency back to its original solid, rigid state. As the material cools, it also shrinks.
Finally, after the material is solidified, the molded part can then be ejected from the mold cavity. Thus, the mold cavity is opened, and the cooled, molded part is released or ejected from the mold cavity.
When creating an injection molded eyeglass lens, manufacturers often use a mold having a mold cavity that is configured to produce a molded part that has a much larger size than required to produce a lens of a desired size. This molded part, often called a lens blank, generally defines a perimeter that is much larger than the perimeter of the final, cut lens. Once the lens blank is prepared, the lens is cut therefrom. This method is useful because an injection molded lens blank can be shaped to define a variety of desirable geometries, and the lens can be cut from the blank in a manner to inherit the desirable geometry from the blank. For example, the lens blank can be formed as a planar lens blank or it can define a simple or complex arcuate contour, such as that of a portion of the surface of a cylinder or sphere. These principles are illustrated in U.S. Pat. No. 6,168,271, issued Jan. 2, 2001 and titled, Decentered Noncorrective Lens For Eyewear.
After a lens blank is prepared, it is cut to define a lens of a desired, final shape. This step in the preparation of a final lens can involve considering the orientation of the optical axis relative to the final lens, the shape and orientation of the orbital in which the lens will be received, and finally, precisely cutting the lens blank in order to produce a final lens having the desired optical qualities and shape. Thereafter, the excess material of the lens blank is typically discarded. Edge defects on the blank, arising from the molding process, are thus not transferred to the finished lens.
Once the final lens is cut from the blank, the edges of the final lens may be smoothed or polished in preparation for mounting on an eyewear frame. For example, when used with eyewear frames that surround only a portion of the lens, the exposed perimeter of the lens should be smooth in order to be aesthetically and physically acceptable. However, when used with eyewear frames that surround the entire periphery of the lens, the edges of the lens may not need to be polished or smooth. Thus, depending on the application and the eyewear frame with which a final lens will be paired, additional finishing operations may be required after the final lens is cut from the lens blank.